Unzen in Nagasaki Prefecture has the dubious distinction of being Japan’s most lethal volcano. Following an eruption in 1792, one side of the mountain collapsed into the sea, causing a 100 metre high mega-tsunami that resulted in the deaths of 15,000 people. Unzen then behaved itself until 1990, when it began to erupt again. Lava started flowing in May 1991, and there were many intermittent eruptions of super-hot gas and rocks over the next few years. 12,000 people had to move out of home, and 2,000 houses were destroyed. A particularly violent eruption in June 1991 killed 45 scientists and journalists who had ventured into the danger zone. Fortunately, the latest eruption ended in 1995, so it’s now possible to explore Unzen’s volcanic landscape in safety.

Unzen is part of the Unzen-Amakusa National Park, which is Japan’s oldest national park, having been founded in 1934. The 1990s eruption created Heisei Shinzan – a whole new summit which is now the mountain’s highest point. It’s topped with a spectacular lava dome that can be seen from several viewpoints around the park. There’s also a cable car that will take you up to the Myoken-dake summit, from where you can get amazing views of the lava flows. From the city of Shimabara on the east side of the volcano, you can still see the ominous hole in the mountain left by the landslide that created the 1792 tsunami.

This is smelly and sulphurous Jaken Hell. Don’t get too close if you don’t want to get scalded!

On the southwest side of the mountain is a hot spring resort that has been a popular tourist destination for hundreds of years, partly because, at 700 metres above sea level, it remains nicely cool during Japan’s hot and muggy summers. There are over 30 hot springs throughout Unzen, many of which you can safely bathe in, a couple for only ¥100 a time. Others are known as ‘hells’ and are much too hot for bathing – some up to 90°C. During the 200 years when Christianity was illegal and Japan was closed off to the outside world, Christians were thrown into these as a particularly unpleasant form of execution. Nowadays you can observe them safely from the sidelines, no matter what your religion.

To get to Unzen, take a bus from Isahaya Station in Nagasaki Prefecture to Unzen Koen Park. (The journey takes around one hour and fifteen minutes.) If you’re coming from Tokyo or Osaka it’s best to fly to Nagasaki airport and then take the bus. You can also take a half-hour ferry trip from Kumamoto Port to Shimabara. For more information, check out Unzen Geo-park’s official website.